3.11. Understanding File Types

The term File Types
describes the collection of associations between documents and the
applications that use them. The most apparent use of this feature is
that, for example, Windows knows to run Notepad when you double-click
on a file with the .txt extension. The
traditional method for configuring these associations to suit your
needs is discussed in Section 4.2.2 in
Chapter 4, but it goes quite a bit deeper
than that.

It all starts with file extensions, the letters (usually
three) that follow the period in most filenames. For example, the
extension of the file Readme.txt is
.txt, signifying a plain text file; the
extension of Resume.wpd is
.wpd, signifying a document created in
WordPerfect. By default, Windows hides the extensions of registered
file types in Explorer and on the desktop, but it's best to
have them displayed.